There are few truly non-invasive tests available to measure left ventricular diastolic function in patients with cardiac disease. In this study we utilized pulsed Doppler to assess transmitral flow-velocity patterns and characterize left ventricular filling and relaxation in 67 patients with hypertrophic cardiomyopathy and 35 normal controls. Patients with hypertrophic cardiomyopathy differed distinctly from normals with prolonged rapid diastolic filling, shortened diastasis, enhanced filling during atrial systole, (reduced ratio of peak flow-velocity in early diastole to that in atrial systole) and prolonged isovolumic relaxation. Abnormal left ventricular filling was present in 48 (72%) of 67 patients with hypertrophic cardiomyopathy, but was more common in symptomatic (25/27, 93%) than asymptomatic patients (23/40; 57%; p less than 0.01) and more frequent in obstructive (17/19, 90%) than in nonobstructive hypertrophic cariomyopathy (31/48, 65%); p less than 0.05). These findings demonstrate that pulsed Doppler echocardiography may be used to quantitatively assess left ventricular function and that impairment in left ventricular filling and relaxation are common and clinically important abnormalities in a population of patients with hypertrophic cariomyopathy.